Abstract: The definition of anti-HLA antibody profile in highly sensitized patients on a waiting list is crucial
when virtual crossmatch is used in organ allocation systems, but also when used to
identify the true deleterious anti-HLA antibodies. Here we propose different levels of risk
based on the results of anti-HLA antibody testing in neat serum (N) and after sera dilution
(DIL) and C1q test in 18 highly sensitized patients. This group was heterogeneous in terms
of anti-HLA antibody titers and their ability to fix complement. After dilution, 15 out of 18
patients (83.3%) showed a reduction of positive bead counts whereas 4 patients showed a
prozone effect and complement fixation was demonstrated. The high dilution of sera and
ascertaining the complement fixation allow the accurate definition of risk anti-HLA antibody
profiles in highly sensitized patients, as demonstrated in 5 of the sensitized patients who
were transplanted.
